linux-kernel - Re: [PATCH 08/10] media: uvcvideo: Always return a value on V4L2_CTRL_WHICH_DEF

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Date:   Thu, 11 Mar 2021 18:21:54 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, senozhatsky@...omium.org
Subject: Re: [PATCH 08/10] media: uvcvideo: Always return a value on
 V4L2_CTRL_WHICH_DEF_VAL

Hi Ricardo,

Thank you for the patch.

On Thu, Mar 11, 2021 at 01:20:38PM +0100, Ricardo Ribalda wrote:
> Fixes v4l2-compliance:
> Control ioctls (Input 0):
>                 fail: v4l2-test-controls.cpp(813): doioctl(node, VIDIOC_G_EXT_CTRLS, &ctrls)
>         test VIDIOC_G/S/TRY_EXT_CTRLS: FAIL
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_v4l2.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 9b6454bb2f28..b500356fd06c 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -1057,12 +1057,7 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
>  			struct v4l2_queryctrl qc = { .id = ctrl->id };
>  
>  			ret = uvc_query_v4l2_ctrl(chain, &qc);
> -			if (ret < 0) {
> -				ctrls->error_idx = i;
> -				return ret;
> -			}
> -
> -			ctrl->value = qc.default_value;
> +			ctrl->value = (ret < 0) ? 0 : qc.default_value;

That's not great, if an error occurs, it should be reported to the user,
not ignored silently. Sounds like this needs to be addressed in
v4l2-compliance, as the V4L2 specification doesn't forbid errors being
returned from V4L2_CTRL_WHICH_DEF_VAL.

>  		}
>  
>  		return 0;

-- 
Regards,

Laurent Pinchart